Silesia thus became the bone of contention between Frederick II and Maria Theresa. Silesia covered the fertile valley of the upper Oder, separating the Slavic Czechs of Frederick's Bohemia on the west from the Slavic Poles on the east. Its population, which was largely German, was as numerous as that of the whole kingdom of Prussia, and if annexed to the Hohenzollern possessions would make them overwhelmingly German. On the other hand, the loss of Silesia would give Austria less direct influence in strictly German affairs and would deprive her of a convenient point of attack against Berlin and the heart of Prussia.
[Sidenote: Outbreak of the War of the Austrian Succession, 1740]
Trumping up an ancient family claim to the duchy, Frederick immediately marched his army into Silesia and occupied Breslau, its capital. To the west, a combined Bavarian and French army prepared to invade Austria and Bohemia. Maria Theresa, pressed on all sides, fled to Hungary and begged the Magyars to help her. The effect was electrical. Hungarians, Austrians, and Bohemians rallied to the support of the Habsburg throne; recruits were drilled and hurried to the front; the War of the Austrian Succession (1740-1748) was soon in full swing.
[Sidenote: Entrance of Great Britain and Spain]
A trade war had broken out between Great Britain and Spain in 1739, [Footnote: Commonly called the War of Jenkins's Ear. See above, p. 311] which speedily became merged with the continental struggle. Great Britain was bent on maintaining liberal trading privileges in the Belgian Netherlands and always opposed the incorporation of those provinces into the rival and powerful monarchy of France, preferring that they should remain in the hands of some distant and less-feared, less commercial power, such as Austria. Great Britain, moreover, had fully recognized the Pragmatic Sanction and now determined that it was in accordance with her own best interests to supply Maria Theresa with money and to dispatch armies to the Continent to defend the Netherlands against France and to protect Hanover against Prussia. On the other side, the royal family of Spain sympathized with their Bourbon kinsmen in France and hoped to recover from Austria all the Italian possessions of which Spain had been deprived by the treaty of Utrecht (1713).
The main parties to the War of the Austrian Succession were, therefore, on the one hand, Prussia, France, Spain, and Bavaria, and, on the other, Austria and Great Britain. With the former at first joined the elector of Saxony, who wished to play off Prussia against Austria for the benefit of his Saxon and Polish lands, and the king of Sardinia, who was ever balancing in Italy between Habsburg and Bourbon pretensions. With Austria and Great Britain was united Holland, because of her desire to protect herself from possible French aggression.
[Sidenote: Course of the War]
The war was not so terrible or bloody as its duration and the number of contestants would seem to indicate. Saxony, which inclined more naturally to Austrian than to Prussian friendship, was easily persuaded by bribes to desert her allies and to make peace with Maria Theresa. Spain would fight only in Italy; and Sardinia, alarmed by the prospect of substantial Bourbon gains in that peninsula, went over to the side of Austria. The Dutch were content to defend their own territories.
[Sidenote: Success of Frederick]
Despite the greatest exertions, Maria Theresa was unable to expel Frederick from Silesia. Her generals suffered repeated reverses at his hands, and three times she was forced to recognize his occupation in order that she might employ all her forces against her western enemies. By the third treaty between the two German sovereigns, concluded at Dresden in 1745, Silesia [Footnote: Except a very small district, which thereafter was known as "Austrian Silesia.">[ was definitely ceded by Austria to Prussia. Frederick had gained his ends: he coolly deserted his allies and withdrew from the war.